LHCb: Time-dependent CP violation in $B^0 \to \pi^+\pi^-$ and $B^0_s \to K^+ K^-$ decays at LHCb

Using an integrated luminosity of 0.69 fb$^{-1}$ collected by LHCb in 2011, we report measurements of direct and mixing-induced CP violation in $B^0 \to \pi^+\pi^-$ and $B_s^0 \to K^+K^-$ decays. The measurements of the $B^0 \to \pi^+\pi^-$ asymmetries are compatible with those from the B factories and yield 3.2$\sigma$ evidence of mixing-induced CP violation, whereas the $B^0_s \to K^+ K^-$ asymmetries are measured for the first time ever.